CN105191332A - Method and device to embed watermark in uncompressed video data - Google Patents

Abstract

It is an object of the present invention to apply a watermark to content received at a client device, more particularly to uncompressed video content. The present invention relates to a method for watermarking uncompressed content received at a client device, said uncompressed content being in compressed form and encrypted by at least one content key (CW), said content key A key (CW) and a watermark instruction form CAS data, the CAS data is encrypted with a sending key and includes at least one signature for authenticating the CAS data, the client device includes: a conditional access module (CAS), a management The CAS data, a descrambler (DSC), has an input for receiving encrypted compressed content, and an output for producing compressed content, and a decoder for converting the compressed content into uncompressed content, watermark inserter (201), connected to the output of said decoder, security activation module (202), connected to said watermark inserter (201), security element (SE? 200), connected to said watermark inserter A device (201) and a security activation module (202), the method includes the following steps: - receiving the CAS data, - decrypting the CAS data by the conditional access module (CAS) using the sending key, - verify the signature of said CAS data, and if said signature is valid, - transmit said content key (CW) to said descrambler (103) and transmit said watermark to said security activation module (202) instructions, - transmit said watermark instructions and a unique identifier to said watermark inserter (201), - enable or disable by said watermark inserter (201) the use of watermark data initialized by said unique identifier to send from said watermark inserter (201) Watermarks the uncompressed content received by the decoder described above.

Description

Method and apparatus for embedding watermark in uncompressed video data

Background technique

Using a watermarking scheme on the uncompressed domain is preferable since the watermarking is done in the client alone, and since it is done in the uncompressed domain, it usually provides the best watermark insertion capability and better invisibility.

But the work after the decoder (for uncompressed watermarks) provides no interaction with the security element linked to the descrambling of the data, thus occurring before the decoder.

Document US 2010/128871 describes a solution in which an auxiliary stream is generated comprising data allowing reconstruction of the main stream and at the same time marl to the reconstruction stream. Therefore, the same stream contains scrambled data and watermarked data. On receive, process the stream as a set of data to be replaced in the modified stream.

Document EP2391125 describes a solution that allows a single marker (at the receiving device) based on a stream that is common to all devices. Control objects contain original values, substitute values, and positions. The security unit determines the arithmetic operation to be applied on the substitute value to obtain the original value. Altering the arithmetic operation according to the internal parameters of the receiving device so that the arithmetic operation will be unique per device, allowing tracking of the device if the stream of descrambled data is analyzed.

Contents of the invention

In the proposed solution, the same content object includes the key to descramble the main content and the tagged data. This is only appropriate if the same unit is responsible for both operations and requires a specific descrambler module capable of performing both operations.

It is an object of the present invention to apply a watermark to content received by a client device, especially when the unit responsible for descrambling is independent of the unit responsible for watermarking.

The present invention relates to a method for watermarking uncompressed content received at a client device, said uncompressed content being in compressed form and encrypted by at least one content key (CW), said A content key (CW) and a watermark instruction form CAS data, the CAS data is encrypted by a sending key and includes at least one signature for authenticating the CAS data, the client device includes:

- a conditional access module (CAS), managing said CAS data,

- a descrambler (DSC) having an input for receiving encrypted compressed content and an output for generating compressed content,

- a decoder for converting said compressed content into uncompressed content,

- a watermark inserter (201), connected to the output of said decoder,

- a security activation module (202), connected to said watermark inserter (201),

- a security element (SE200), connected to said watermark inserter (201) and security activation module (202),

The method comprises the steps of:

- receiving said CAS data,

- decrypting said CAS data by said conditional access module (CAS) using said sending key,

- verify the signature of said CAS data, and if said signature is valid,

- then transmit said content key (CW) to said descrambler (103) and said watermark instructions to said security activation module (202),

- transmitting said watermark instructions and a unique identifier to said watermark inserter (201),

- enabling or disabling, by said watermark inserter (201 ), watermarking of uncompressed content received from said decoder with watermark data initialized by said unique identifier.

Description of drawings

The invention will be better understood with reference to the accompanying drawings, in which:

Figure 1 represents the watermarking of uncompressed content following only the video decoder,

Figure 2 represents the watermarking of uncompressed content input into HDMI,

Figure 3 shows the exchange of messages between SE and SA,

Figure 4 shows an alternative embodiment of message exchange between SE and SA.

Detailed ways

Conditional access data includes content (video or audio data or a combination thereof) encrypted by one or more content keys, and includes CAS data, ie data allowing decryption of the encrypted content. The CAS data also includes conditional access conditions associated with the content describing the conditions to be encountered by the decoder to decrypt the content. Conditional access data is broadcast, unicast, or sent upon receipt of a request. The CAS data may also include watermark instructions to be passed to the watermark inserter.

Once received in the decoder, the CAS data is extracted from the conditional access data and forwarded to the conditional access module (CAS in Figures 1 and 2), which is responsible for enforcing the security measures defined in the conditional access condition . This module can have several forms, namely a physical module or a software module. A known solution is in the form of a smart card with interface 7816, but the invention is also applicable to other forms of units or interfaces such as USB, LVDH, PCMCIA. The module CAS can also be integrated into the security element SE.

This module includes the keys necessary to decrypt the CAS data and to extract from the CAS data the key (CW) to decrypt the content. In addition to the key, this module extracts the conditions (use rules) and transmits the key and the conditions to the security element SE. Note that the communication between the CAS and SE is encrypted and protected by keys initialized on both units.

Messages exchanged between CAS and SE can be signed, i.e. a digest of the payload (e.g. watermark instructions, nonce, and identifier) is computed by the CAS (e.g. using a hash function) and encrypted by a signing key to generate a signature . The signature is added to the message and the message is preferably encrypted with the sending key. On the receiving side, the message is first decrypted and the digest is computed on the payload. With the key corresponding to the signing key, the received signature is decrypted and the result is compared to the calculated digest. If these two values are the same, the message is authentic. The signing key can be a symmetric key or an asymmetric key (public/private key).

In conventional circumstances, the key obtained by the CAS is transmitted to the descrambler DSC responsible for decrypting the content. Once the content is decrypted, it is processed by a decoder to produce uncompressed content. The watermarking module WMK receives uncompressed content and applies a watermark, which is parameterized by a unique identifier of the decoder.

The proposed solution is to have a secure link between the Security Element (SE) 200 (cf. Fig. 1 ) and the uncompressed domain watermarking unit 201 provided by the CAS environment.

According to Fig. 1, the SE 200 relays the CAS data, which introduces an explicit dependency between the successful descrambling operation and the activity of the block located after the decoder, namely the watermark inserter.

SE200 also provides other sensitive information (such as device unique ID, CAS module ID, ID contained in CAS data or key). This information, if sent in plain text to the watermark inserter, may be intercepted and modified. That's why the connection between these two blocks must be secure.

Here, the watermark inserter 201 inserts information (watermark payload) into audio and/or video content. This payload is independent of the unique identifier received from the CAS. It can then be bypassed by hackers (audio and/or video content not sent to the watermark block), or the payload (watermark data) can be modified. The watermark inserter can be placed just after the trace decoder, or along the transmission line between the decoder and the final display or TV screen, like an HDMI sender.

The proposed solution ensures:

- A way to ensure that the watermark inserter 201 is not bypassed and thus activated if decided by the CAS. If the watermark inserter 201 does not appear to be activated, the SE 200 stops descrambling the content.

- A way to ensure communication between SE 200 and watermark inserter 201, so that watermark inserter 201 confidently accesses the information it needs at time T, such as the payload necessary to insert into the content. SE 200 manages all or part of the calculation of the information to be inserted. In general, this information is: a unique identifier (UID) representing the decoder or CAS module, a timestamp (T), and any other information of interest like specific information about the content itself (SID). The payload is calculated from this data before being inserted into the content. The goal of this operation is to protect the payload from attack or transmission errors (by computation of ECC or collusion resistant codes such as Tardoscode).

All or part of this payload must then be used by the watermarking system to be inserted into the content.

The proposed solution is to add a security activation block 202 which activates/deactivates the watermark inserter 201 . For security reasons, it is recommended to implement the security activation block 202 and the watermark inserter 201 just after the video decoder and in a Trusted Execution Environment (TEE). Access between the security activation block 202 (SA202) and the watermark inserter 201 is not possible from the host CPU of the client device.

The security activation block 202 is controlled by some registers accessible eg via a private bus as shown in FIG. 1 or via a public bus (AMBAAPB) as shown in FIG. 2 . Security activation block 202 is capable of enabling/disabling at least two features: watermark on video content, watermark on audio content, or a combination thereof. In Figures 1 and 2, the security activation block 202 and the watermark inserter 201 are connected on the video content.

The main concept relies on the fact that the security activation block 202 has to receive messages called Activation Messages (AM) from the SE 200 to activate/deactivate different features. AM is also used to send the payload necessary to mark content. Another feature performed by the security activation block 202 is a secure link with SE 200 for exchanging sensitive information. For example, SE 200 may send security settings to security activation block 202 . The security activation block 202 will then send them to the watermark block 201 .

The main attack is for a person to record the message and thus be able to activate or deactivate the features according to his desire. This attack is called a "replay attack".

A secondary attack is where the attacker attempts to modify the content of the message. Thus, when the SE 200 generates the AM, it should be encrypted and signed for the security activation block 202 . Additionally, AM should embed random numbers from a true random number generator (TRNG). An example of AM is shown in FIG. 3 . It should contain at least nonce, activation token, payload (including UID), payload size and signature.

Figure 2 depicts an example where a device is using HDMI and the watermark block 201 on the device must be activated. The conditional access system (CAS) will receive the CAS data. According to this example, the CAS data is in the form of an entitlement control message ECM. These ECMs contain encrypted CWs and their usage rules. The encrypted CW and its usage rules are sent to SE200. The usage rules indicate to the SE 200 that the current video content must be watermarked.

During initialization phase the SE 202 and SA 202 share a public key stored in each device. This key will be used to encrypt the messages exchanged so that the content cannot be accessed by third parties. Since communications between these two units can be intercepted by third parties, it is important to implement a mutual authentication protocol. Each party should make sure to speak to the other party and not utilize an emulator.

The message sent to the security activation module (202) contains watermark instructions. In case of activation, the identifier to be embedded in the content is included in the message.

Then, the following steps can be performed according to FIG. 3 .

1. The CAS receives the ECM containing the encrypted Control Word (CW) and its usage rules or access conditions.

2. SE200 decrypts CW and its usage rules. The rules of use state that eg a DVB-CSA descrambler should be used to decrypt said content and a watermark should be activated on the video. At the same time, SE200 generates an activation message (AM) and adds variable values. This variable value should change for each message generated by the security activation block 202 . It can be a random number, a counter incremented by 1 at every message or timestamp. This value is stored to SE200. AM is encrypted and signed. The AM is then sent to the security activation block 202 .

3. The security activation block 202 decrypts and authenticates the AM. If the authentication is successful, security activation block 202 checks the mutable value to determine if the received value has changed from a previous value. In the case of a counter, the variable value received should be higher than the most recently received variable value. The same applies to timestamps, which should be advanced for newly received timestamps compared to those received in previous messages. For nonces, the security activation block 202 should store all previously received nonces (or at least a predefined number such as the most recent 20) to compare received nonces with the value contained in the message.

In case the variable value does not comply with one of the above mentioned rules, the message is rejected. Otherwise, the security activation block 202 activates the above features according to the content of the AM. After authentication, the security activation block generates an acknowledgment message (ACKM) that is encrypted and signed. This ACKM is sent back to SE200. It should contain at least the same nonce as AM, and it should also contain Activation Flag, Payload (UID), Payload Size, ACK Flag and Signature. The random number is then stored by the security activation block 202 to avoid presenting the same message at a later time.

4. SE200 decrypts and authenticates the ACKM. ACKM should contain the same nonce as the one in AM. If the ACKM was not properly authenticated, was not received on time (using a watchdog), or the nonce is different from what was entered in the previous AM, the transmit watermark command is considered a failure and SE 202 stops sending messages to the descrambler The device provides CW.

Commonly, security activation block 202 does not include persistent storage. Thus it is not possible to store the most recent mutable value for accurate anti-replay verification. This is why Figure 4 shows another approach. Note that this method can be applied even if SE 202 contains persistent storage.

1. SE 200 sends a first message (AM) to security activation block 202, informing that an indication message will be sent. At this stage, the first message may be encrypted or in plaintext. This message may contain a signature that allows SA 202 to authenticate the first message. In the example of Fig. 4, this message is an activation message AM.

2. In case the message is encrypted and signed, SA 202 decrypts and verifies the signature. If the signature is correct, SA202 generates a random number X and sends a second message ACKM containing the random number X to SE200. Random number X is stored by SA202. At this stage, the second message may be encrypted or in plaintext. This second message is preferably encrypted and contains a signature to ensure that only genuine SA 202 can generate it.

3. At the same time SE 202 receives and decrypts (if encrypted) message ACKM, SE 202 extracts the random number. Using the random number and watermark instructions, SE 202 prepares a message, encrypts and signs it. Where the instruction refers to disabling a watermark on the content, the message need not contain an identifier. Send this message to SA202.

4. Then, SA202 decrypts and verifies the signature. If the signature is correct, it also verifies that the nonce X is the same as the previously stored value. If it is different, the message is rejected. When these controls have been passed, the watermark instructions contained in the message can be executed.

5. Then, SA202 prepares the final confirmation message FACKM to confirm the execution of the watermark instruction. This message will contain the nonce X and is also encrypted.

6. SE200 receives the FACKM and once decrypted, extracts the state of SA202. If SA 202 confirms successful completion of the watermark command, SE 2002 may transmit the content key to the descrambler.

Claims (6)

1. one kind for adding the method for watermark to the unpressed content received at client device place, described unpressed content to be in the form of compression and to be encrypted by by least one content key (CW), described content key (CW) and watermark instruction form CAS data, described CAS data are passed through to send secret key encryption and are comprised at least one signature for CAS data described in certification, and described client device comprises:

-conditional access module (CAS), manages described CAS data,

-descrambler (DSC), has the output of the input of the content of the compression for receiving encryption and the content for generation of the compression of deciphering,

-decoder, the Content Transformation for the compression by described deciphering becomes unpressed content,

-watermark inserter (201), is connected to the output of described decoder,

-safe activation module (202), is connected to described watermark inserter (201),

-safe unit (SE200), is connected to described watermark inserter (201) and safe activation module (202),

Said method comprising the steps of:

-receive described CAS data,

-utilize CAS decrypt data described in described transmission double secret key by described conditional access module (CAS),

-verify the signature of described CAS data, and if described signature is effective,

-then transmit described watermark instruction to described safe activation module (202),

-only just transmit described content key (CW) to described descrambler (103) when the transmission success of described watermark instruction,

-transmit described watermark instruction to described watermark inserter (201),

-to be enabled or disabled by described watermark inserter (201) and add watermark to the unpressed content from described Decoder accepts.

2. method according to claim 1, wherein comprises the following steps from described safe unit (SE200) to described safe activation module (202) transmission watermark instruction:

-ask random number (X) by described safe unit (SE200) from described safe activation module (202),

-generate this random number (X) by described safe activation module (202), store described random number (X) and described random number (X) is sent to described safe unit (SE200),

-prepare message by described safe unit (SE200), described message at least comprises described watermark instruction, random number and the signature in described watermark instruction and random number,

-send this message to described safe activation module (202),

-verify that whether described signature is true and whether described random number is identical with the random number previously sent by described safe activation module (202), and when for being, accept described watermark instruction, and

-send final acknowledge message to described safe unit (SE200), have successfully completed described transmission to inform to described safe unit (SE200).

3. method according to claim 1 and 2, wherein said safe activation module (202) and watermark inserter (201) are arranged in the environment of trust, cannot access the connection between these two unit outside the environment of described trust.

4. according to the method described in claims 1 to 3, wherein said CAS data comprise unique identifier, while adding watermark described in enabling, described identifier is transferred to described safe activation module (202) and watermark inserter (201) together with described watermark instruction, and described identifier defines the payload for adding watermark to described content.

5. a client device, comprising: conditional access module (CAS), is responsible for receiving CAS data, and to described CAS decrypt data to obtain watermark instruction and content key (CW), descrambler (DSC), has the output of the input of the content of the compression for receiving encryption and the content for the compression based on described content key generation deciphering, decoder, the Content Transformation for the compression by described deciphering becomes unpressed content, watermark inserter (201), is connected to the output of described decoder, to insert watermark based on described watermark instruction, safe activation module (202), is connected to described watermark inserter (201), safe unit (SE200), be connected to described conditional access module (CAS), descrambler (DSC) and safe activation module (202), it is characterized in that, described conditional access module (CAS) has the device of the signature for verifying described CAS data, and the device had for described watermark instruction to be transferred to described safe activation module (202) in the effective situation of described signature via described safe unit (SE200), described safe unit (SE200) has for verifying whether described watermark instruction is successfully transmitted the device of described watermark inserter, and the device had for described content key being transferred to when Successful transmissions described descrambler (103).

6. client device according to claim 5, wherein said safe activation module (202) comprises the random number generator that can produce random number (X), described safe activation module (202) generates, store described random number, and described random number is sent to described safe unit (SE200), described safe unit (SE200) prepares message, described message at least comprises described watermark instruction, random number, and the signature in described watermark instruction and random number, described safe activation module (202) has such device, this device is for verifying that whether described signature is true, and whether described random number is identical with the random number stored, when for being, accept described watermark instruction, and send final acknowledge message to described safe unit (SE200), described transmission is have successfully completed to inform to described safe unit (SE200).